This invention relates in general to pneumatic reciprocators for automatically reciprocating, i.e. moving an object back and forth, and specifically to pneumatic reciprocators for use with machine tools such as surface grinders.
Professional type surface grinders are tools in which a grinding wheel is held stationary with respect to a movable workpiece for performing precise machining operations on the workpiece. To secure the workpiece to the movable table of the surface grinder, a magnetic chuck mechanism is conventionally used. The surface grinder table is controllable by a machinist to perform precision work in three dimensions; length, width and depth. A surface grinder is used to produce very fine finished surfaces and therefore the movable table must provide stability and precision movement. It is thus quite massive. Crank wheels are used by the machinist to move the table horizontally in and out, in addition to an adjustment device for moving the grinding wheel vertically. During a finishing operation, moving the table horizontally back and forth requires a great deal of physical effort by the machinist. While certain surface grinders include mechanisms for automatically reciprocating (i.e. moving the table back and forth), the mechanisms are complex and quite expensive. Indeed, the cost of a surface grinder with an automatically reciprocating table is about double the cost of a surface grinder without that feature.
With the invention, a very simple, low cost attachment is provided for automatically reciprocating the movable table on a surface grinder. The distance or stroke of the table is determined by the machinist. The inventive device is pneumatically operated, requires no electrical connections, and is readily mounted on a standard surface grinder. With the invention, the very tiring cranking required of the machinist is totally eliminated.
The automatic reciprocator of the invention utilizes a novel combination of elements that include a standard off-the-shelf air cylinder assembly that is modified slightly and fitted within a cylindrical manifold, over which a sleeve valve is movably mounted. The reciprocator assembly is affixed to the base of the surface grinder and the piston rod of the air cylinder is connected to the movable table. A pair of adjustable stops carried by the table control the stroke or travel distance of the table by displacing the movable sleeve valve on the manifold to open and close sets of cylindrically arranged air holes in the manifold for reversing the direction of piston movement.
A feature of the invention is the relative spacing of the resilient seals carried by the sleeve valve relative to the sets of air holes which cooperate to provide pneumatic cushioning of the massive table. Another feature is the vented dust boots sealing the movable sleeve valve to the manifold which are always under positive pressure to keep dust and abrasives from the movable parts.